Palladium(II) has been extensively investigated since the late nineteenth century and it has long been recognized that Pd(II) has a coordination number of 4. The coordinated groups, often referred to as ligands, serve as electron donors. Those ligands having two atoms which can simultaneously serve as donors are referred to as bidentate ligands. Chelate ligands, or ring-forming groups, are an important class of bidentate ligands. Such a chelate ligand is the acetylacetonato ion, also referred to as the acetylacetonate anion (often designated as ACAC hereinafter), and may be represented by the structure: ##STR1## The acetylacetonate anion is derived from the enol form of 2,4-pentanedione (a beta-diketone) which exists in equilibrium with its keto form according to the equation: ##STR2## Loss of the hydroxy hydrogen of the enol form of 2,4-pentanedione results in the formation of the ACAC anion. Two such ACAC anions coordinate with Pd(II) to form the coordination compound palladium(II) bis(acetylacetonate): ##STR3## The hexafluoroacetylacetonate anion, wherein each CH.sub.3 above is replaced by CF.sub.3, will be referred to herein as F.sub.6 ACAC.
General descriptions of the metal complexes of beta-diketones are available: see Fernelius, Ed., Inorganic Syntheses, Vol. II, pp. 10-20, McGraw Hill Book Company, Inc., New York (1946) and Sievers and Sadlowski, "Volatile Metal Complexes", Science 201, 217-223 (1978). In these publications, compounds such as aluminum(III) tris(acetylacetonate) and chromium(III) tris(acetylacetonate) are called metal complexes.
Pd(ACAC).sub.2 and Pd(F.sub.6 ACAC).sub.2 have been disclosed in Okeya et al., Chem. Lett., 1305 (1977) and Okeya et al., J. Chem. Soc. Chem. Comm., 914 (1977), but no characterization or physical properties of Pd(F.sub.6 ACAC).sub.2 are given.
Metal complexes with fluorinated beta-diketones have been described in Sievers and Sadlowski, supra, although Pd(F.sub.6 ACAC).sub.2 is not mentioned.
The two Okeya et al. papers, supra, disclose Pd(F.sub.6 ACAC).sub.2.(bipyridine).sub.2 and the six tetrakis compounds Pd(F.sub.6 ACAC).sub.2.(ammonia).sub.4, Pd(F.sub.6 ACAC).sub.2.(methylamine).sub.4, Pd(F.sub.6 ACAC).sub.2.(ethylamine).sub.4, Pd(F.sub.6 ACAC).sub.2.(n-propylamine).sub.4, Pd(F.sub.6 ACAC).sub.2.(ethylenediamine).sub.2, and Pd(F.sub.6 ACAC).sub.2.(pyridine).sub.4. Okeya et al. refer to these compounds as palladium(II) amine complexes.
Bis(hexafluoroacetylacetonate) compounds of nickel(II) and cobalt(II) are known. See Parshall, Ed., Inorganic Syntheses, Vol. XV, pp. 96-100, McGraw Hill Book Company, Inc., New York (1974).
U.S. Pat. No. 3,356,527 discloses vapor plating metals from hexafluoroacetylacetonate compounds of copper, nickel, cobalt, and lead. The patentee suggests that palladium(II) bis(hexafluoroacetylacetonate) appears to have plating potentialities. Such a utility differs from that of the present invention wherein elemental palladium, derived from the palladium(II) bis(hexafluoroacetylacetonate) adducts, is useful as a primer in the electroless plating of other metals. The patentee makes use of 250.degree.-500.degree. C. in the vapor plating process whereas the present invention utilizes temperatures for reduction of the adduct that are below about 150.degree. C.
U.S. Pat. Nos. 3,770,785, 3,876,675 and 3,883,570 disclose bis-chelate derivatives of palladium.
U.S. Pat. No. 3,876,675 discloses fluoroalkyl beta-diketones; however, the compounds described contain two different chelate groups for the palladium atom, one of which may be the hexafluoroacetylacetonate chelate.
U.S. Pat. No. 4,042,603 discloses intramolecular cyclization of substituted diphenylether or benzophenone in the presence of a carboxylic acid salt of palladium and/or palladium organic complexes. Pd(ACAC).sub.2 is listed as a palladium organic complex. Certain components (called promoters) are added with the catalyst in order to increase the yields. Among these are listed acetylacetone and hexafluoroacetylacetone.
U.S. Pat. No. 3,946,057 teaches a process for preparing metal compounds of organic radicals, including Pd(F.sub.6 ACAC).sub.2, utilizing a metal halide, a beta-diketone, an alkylene oxide and a polar solvent.
U.S. Pat. No. 3,538,002 discloses the use of beta-diketone metal complexes to reduce oxidation of functional fluids. Palladium bis(hexafluoroacetylacetonate) is included in the specification.
U.S. Pat. No. 3,318,891 discloses complexes of palladium(II) acetate, benzene, pyridine, aniline, benzylamine, quinoline, 2-aminopyrimidine and benzidine.
Although the existence of Pd F.sub.6 ACAC).sub.2 is disclosed in the literature, there is no characterization of it or description of its physical properties. However, both Pd(ACAC).sub.2 and Pt(ACAC).sub.2 are reported and characterized.
Although Pd(F.sub.6 ACAC).L.sub.n, wherein L is a Lewis base and n is an integer from 1 to 4, is disclosed in the Okeya et al. papers, supra, for bipyridine (n is 2) and for ammonia, primary amines, and pyridine (n is 4), the preparation of Pd(F.sub.6 ACAC).sub.2 is not described. Similarly, Pt(F.sub.6 ACAC).sub.2.(pyridine).sub.4 is disclosed but the preparation of the parent compound is not described.
The prior art refers to compounds having formulas such as Pd(F.sub.6 ACAC).sub.2.L.sub.n and Pd(F.sub.6 ACAC).sub.2 as complexes. To avoid misunderstanding, compounds having the formula Pd(F.sub.6 ACAC).sub.2.L.sub.n will be referred to herein as adducts.